Printers for continuous printed sheets which are printed with UV ink and subsequently hardened are known in the prior art. The term UV ink denotes in the following an ink which can be polymerized, that is, hardened under the influence of UV rays. The surface of the printed sheet also becomes dry and touchable at the same time as the curing of the ink. The printed sheets can be supplied to the printer as individual printing sheets or as so-called endless printing webs from a roll. The ready, printed sheet, i.e. the printing product, can be subsequently further processed, stacked or, in the case of endless printing webs, wound up again, for example, on a receiving roll. The curing, which is used here synonymously with a thorough curing or thorough polymerization, takes place immediately after the printing in order to prevent a smearing during the further processing or a so-called transfer of the printed front side onto the non-printed back side of the printed product during the stacking or rolling up of the latter. To this end, the freshly printed printing product is irradiated with a UV lamp. In order to ensure the UV curing in continuous systems in the required short time, correspondingly high UV irradiation performances are necessary which also thermally stress the printing product. The thermal stress by the strong, long-wave range of traditional UV irradiators could be reduced by using LED-UV irradiators and air cooling of the surface of the irradiated printing product; however, this is too high a load, e.g., for thin and/or thermally sensitive plastic sheets which can result in distortion, formation of folds or even a melting or catching fire of the printed sheet. The situation is additionally intensified by the exothermal reaction enthalpy released during the polymerization of acrylate inks.
The present invention has the goal, among other things, of eliminating the above-described disadvantages of the prior art and to make available a method and a curing chamber and a printer operated with a corresponding curing chamber with which even then plastic substrates, in particular plastic sheets, e.g., of polyethylene (PE) or polyvinyl chloride (PVC) are printed with UV ink and can be hardened in continuous systems even at high through speeds.